Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.77   10.561%   $53.9206   $53.92   $53.90   $53.90  
  Purchase #2 $78.42   5.272%   $82.5543   $82.55   $82.55   $82.60  
  Purchase #3 $12.57   4.235%   $13.1023   $13.10   $13.10   $13.10  
  Purchase #4 $163.89   11.332%   $182.462   $182.46   $182.45   $182.50  
  Purchase #5 $232.61   6.618%   $248.0041   $248.00   $248.00   $248.00  
  Purchase #6 $16.54   12.126%   $18.5456   $18.55   $18.55   $18.50  
  Purchase #7 $239.75   9.714%   $263.0393   $263.04   $263.05   $263.00  
  7 purchase totals = $792.55       $861.6282   $861.62   $861.60   $861.60